I brought this up in my post on the Ribble thread yesterday. After another huge winter flood only 4 years since the last one, maybe we need a rethink on hatcheries.
People have been blaming the last couple of poor seasons on washed out redds, due to the floods in December 2015. If that is the case then we can expect the same in another 3 or 4 years after this weekend's floods.
If these extreme weather events are becoming more frequent due to global warming, then maybe we should be doing something to prevent a total wipe out of a years spawning ? Couldn't a hatchery achieve this ?
To some extent it depends greatly on the rivers course itself and where specifically in each river the fish traditionally make the beds. Based on what can be seen thus studied in Alaska the top threats are that the tiny fry who have just recently (prior to event) abandoned the gravel bed and migrated to the shoreline environs are #1 swept away to sea or #2 they are left land locked far from the channel when the water drops. The land locking thing happens here with adult fish as well if they don't stay on or near the bottom during events.
There is the chance of scouring of the bottom if the adult female has placed a bed in the very worst of spots and........ Speaking of bad spots for beds, if the bed is located in a slower flow or on the edge of a current then the deposition of silt onto the developing eggs or alvin still in the nest gravel will kill off the hatch if the silt is heavy enough in its coverage.
For a ray of hope consider this. These fish and where these fish spawn has been fine tuned over at least the past 11 to 12,000 years of development. They use the same areas each spawn for various reasons such as currents, substrate size, etc. The process of elimination has dictated that those nests too close to shore risk desiccation during low water events or anchor ice during extreme cold conditions.
In a nut shell the balance between those who nest well and those who don't has contributed to the species surviving through the millenniums regardless of either mans or natures best efforts to clear them out. In the case of lost beds and fry the result is a 'generational hole' regarding that loss. If the loss were to be total and every bed lost the "hole" will take longer to fill in and reduced harvest on affected waters is one way to assist in such things.
Things seem to be becoming more extreme nowadays. My local river ribble has just recorded record levels in many places, the records were set 4 years ago when we had the last major flood. The river runs through a lot of arrable land which drains very quickly into the streams and into the main river. This seems to cause a very rapid and extreme rise and fall in water levels, like a flash flood. From about 0.5 metres to 6+ metres and back down to 1.5 metres in little over 24 hours !!
Some careful wading will be needed down where I fish when levels drop